1. Field of the Invention
This invention generally relates to methods, devices and systems for determining parameter values of objects and environments and, more specifically, to methods, devices and systems which utilize a voltage reading associated with a common mode signal of a balanced circuit to determine a value of a parameter of an object or an environment.
2. Description of the Related Art
The following descriptions and examples are not admitted to be prior art by virtue of their inclusion within this section.
Many sensors employ balanced circuits for determining information. In particular, a balanced circuit may be configured such that information of interest for a sensor may be determined from a differential voltage between the output nodes of the balanced circuit. More specifically, each line of a balanced circuit may be configured with elements which are operationally sensitive to changes in a parameter of an object or an environment in which the balanced circuit is disposed and each of the elements may be configured to alter the voltage along its respective line in an opposing manner. In general, it is the objective of such balanced circuits to have signal lines of matched impedances such that noise and interference induced in each of the lines does not substantially affect the accuracy of the differential voltage measurement attributed to the information of interest. In particular, having matched impedances on each signal line allows noise and interference signals to be canceled for a differential voltage measurement. On the contrary, any inequality in the noise and/or interference induced in each line will result in such signals not being fully cancelled.
In order to ensure the accuracy of a differential voltage measurement, a common mode voltage between the signal output nodes of the balanced circuit is often monitored. In particular, a common mode voltage of a presumably balanced circuit is monitored relative to a target voltage or relative to the differential gain of the circuit, the latter scenario of which is referred to as a common-mode rejection ratio. The term “common mode voltage” refers to the voltage at a given location that appears equally and in phase from each signal conductor to a common reference. Alternatively stated, the term “common mode voltage” refers to the instantaneous algebraic average of two signals within a balanced circuit with both signals referenced to a common reference. Although both differential mode and common mode signals are analyzed when using a balanced circuit, they are generally referenced as “wanted signals” and “unwanted signals,” respectively. In particular, differential mode signal measurements relate directly to determining the value of a parameter being measured by a sensor and, thus, are considered “wanted.” In contrast, common mode signal measurements reflect the portions of the signals which do not contribute to determining the information of interest for a sensor and, thus, are considered “unwanted.” In other words, common mode signal measurements are only monitored in conventional practices for determining whether to accept or throw out differential mode signal measurements relating to a variable parameter.